http://www.parrotsecrets.com/
The reason all these pages have that look is that each paragraph is designed only to get you to read the next paragraph. The idea is that if you've already decided that you're going to buy it, you'll just scroll down to the bottom. And if you haven't yet decided to buy it, then the next thing that needs to happen before closing the sale is that you need to read the next paragraph. The logic of it actually makes a lot of sense.
These sites spend quite a bit of time perfecting the copyrighting and the small details like making certain headlines have a yellow background. To someone who can't tell a spam site from Facebook it can be pretty effective - assuming your aiming for that market.
The longer the better--12 pages isn't too long.
It's amazing, but it's well-documented.
For something like a $79.95 ebook on parrot training, it would probably take you a fair amount of convincing to buy. That's why they give you a long list of reasons in storytelling format. If it were free, you would need less convincing, and the copy would be drastically shorter.
The core theory is in fact quite simple: People have a (serious) problem to solve and the text presents the product as a solution to these problems by pointing out its benefits. In other words: People are expected to be self-interested.
Of course, potential buyers also wonder whether the product will deliver. Since media is not interactive, you have to deal with typical objections up front. Thus, these latters tend to be rather long.
Next, you'd need the attention of the audience. Thus, you make (lots of sub-) headlines that are easy to scan and makes readers interested. Among others, curiosity is often induced to make people willing to read the rest of the text. "Do you make these mistakes in English" is a classic example. The magic word here is of course "these". It promises an answer in the text without revealing it yet.
In the text, you can use typical sales tactics to overcome buyers' fear of later remorse. Caldini's 'Influence' describes the common 6 tactics.
For example, people tend to buy from people they like. One way to make people like the seller is to point out similarities. Thus, the seller often uses a profile similar to the buyers -- in the above example: "Natalie ('A Parrot Lover For The Last 12 Years')". This also establishes the seller as an authority -- 12 years is quite some time to gain experience and thus she probably knows what she's talking about.
Additionally, you have a clear call to action. For some reason, people are either unable to figure out what to do next or they are willing to obey commands.
And that's it, basically.
As far as I know there's no agreement about an explanation on why these tactics work. Why do people obey commands by authorities? You may construct an explanation based on the different models of economic or biological or psychological behavior.
But it's hard to test which of those (if any) is the one 'true' explanation.